Hydrazone compound and electrophotographic photoreceptor and organic electroluminescent element both containing the same

ABSTRACT

There are provided a hydrazone compound represented by formula (I), an electrophotographic photoreceptor which has a photosensitive layer containing the compound on an electrically conductive support, and an organic electroluminescent element containing the compound as a charge transporting material: ##STR1## wherein Ar 1  represents a substituted or unsubstituted phenylene group, a substituted or unsubstituted naphthylene group, a substituted or unsubstituted biphenylene group, or a substituted or unsubstituted anthrylene group, Ar 2  represents a substituted or unsubstituted aryl group, R 1  and R 2  each independently represents a hydrogen atom, a halogen atom, an unsubstituted alkyl group, or an unsubstituted alkoxy group, R 3  represents an unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted aryl group, Z represents an ethylene group or a vinylene group, and n is 0 or 1.

FIELD OF THE INVENTION

The present invention relates to a novel hydrazone compound useful as acharge transporting material for use in an electrophotographicphotoreceptor, an organic electroluminescent element, and the like. Thepresent invention also relates to an electrophotographic photoreceptorand an organic electroluminescent element both containing the hydrazonecompound.

BACKGROUND OF THE INVENTION

Electrophotography is a kind of image-forming process, which generallycomprises charging the surface of a photoreceptor containing aphotoconductive material in the dark by means of, e.g., coronadischarge, image-wise exposing the resulting photoreceptor toselectively eliminate the charge in the exposed area to thereby obtainan electrostatic latent image, converting the latent image into avisible image using a toner, transferring the toner image to paper,etc., and then fixing the toner particles to obtain an image.

Photoreceptors include inorganic photoreceptors containing an inorganicphotoconductive compound, e.g., selenium, zinc oxide, cadmium sulfide,or silicon, as a major component and organic photoreceptors containingan organic charge generation material and a low- or high-molecularorganic charge transporting material both of which are dispersed in abinder resin. The inorganic photoreceptors each has many advantages andhas been widely used so far. However, those inorganic photoconductivecompounds have the following drawbacks. For example, selenium not onlyis costly because of the difficulty of the production thereof, but alsotends to crystallize and to be readily affected by heat or mechanicalshock to thereby suffer performance deterioration. Zinc oxide andcadmium sulfide are insufficient in moisture resistance and mechanicalstrength, and a dye added as a sensitizer is deteriorated by thecharging and exposure. Thus, photoreceptors containing zinc oxide orcadmium sulfide are defective in durability, etc. Silicon is also costlybecause of the difficulty of the production thereof and because a highlyirritant gas is used for producing the same. Moreover, care should betaken in handling silicon because it is sensitive to moisture.

For the purpose of overcoming the drawbacks of these inorganicphotoreceptors, organic photoreceptors containing various organiccompounds have been investigated in recent years and have come to beused widely. The organic photoreceptors include single-layerphotoreceptors in which both a charge generation material and a chargetransporting material are dispersed in a binder resin and double-layeredphotoreceptors which comprise a charge generation layer and a chargetransporting layer which layers perform their respective functions.Organic photoreceptors of the double-layer type are advantageous in thateach material can be selected from a wide range of compounds and aphotoreceptor having a desired performance can be produced relativelyeasily by selecting a suitable material combination. Because of this, alarge number of investigations have been made on double-layered organicphotoreceptors, which are in wide use.

As the charge generation materials, various kinds of organic pigmentsand dyes have been proposed and put to practical use. Examples thereofinclude azo compounds, bisazo compounds, trisazo compounds, tetrakisazocompounds, thiapyrylium salts, squarilium salts, azulenium salts,cyanine dyes, perylene compounds, metal-free or metal phthalocyaninecompounds, polynuclear quinone compounds, thioindigo compounds, andquinacridone compounds.

Examples of charge transporting materials include the oxadiazolecompounds disclosed in JP-B-34-5466, the oxazole compounds disclosed inJP-A-56-123544, pyrazoline compounds disclosed in JP-B-52-41880, thehydrazone compounds disclosed in JP-B-55-42380, JP-B-61-40104,JP-B-62-35673, and JP-B-63-35976, the diamine compounds disclosed inJP-B-58-32372, stilbene compounds disclosed in JP-B-63-18738,JP-B-63-19867, and JP-B-3-39306, and the butadiene compounds disclosedin JP-A-62-30255. (The terms "JP-B" and "JP-A" as used herein mean an"examined Japanese patent publication" and an "unexamined publishedJapanese patent application," respectively.) Some of the organicphotoreceptors containing these charge transporting materials haveexcellent properties and have come into practical use. However, anyorganic photoreceptor has not been obtained so far which fully satisfiesthe various property requirements which an electrophotographicphotoreceptor is required to meet.

On the other hand, electroluminescent elements containing an organiccompound as a component thereof have conventionally been investigated,but sufficient luminescent properties have not been obtained. In recentyears, however, a multilayered electroluminescent element comprisingseveral kinds of superposed organic materials was found to showsignificantly improved properties. Since then, investigations onelectroluminescent elements containing organic substances have been madeactively. The first multilayered electroluminescent element was reportedby C. W. Tang et al. of Eastman Kodak Corp. (Appl. Phys. Lett. Vol. 51,p. 913 (1987)). In this electroluminescent element, a luminance of 1,000cd/m² or higher was obtained at a voltage of 10 V or lower, showing thatthis organic electroluminescent element has far higherelectroluminescent properties than the conventional inorganicelectroluminescent elements in practical use, which inorganic elementsneed a voltage as high as 200 V or higher.

Such multilayered electroluminescent elements have a structurecomprising superposed layers of an organic fluorescent substance, anorganic substance capable of transporting charges, i.e., a chargetransporting material, and electrodes. When charges (holes andelectrons) are injected from each electrode, the charges move throughthe charge transporting material and recombine to cause luminescence.Used as the organic fluorescent substance are, for example, fluorescentorganic dyes such as 8-quinolinol aluminum complex and coumarin. For useas the charge transporting material, various compounds well known asorganic materials for use in electrophotographic photoreceptors arebeing investigated. Examples of such compounds for use as chargetransporting materials include diamine compounds such asN,N'-di(3-tolyl)-N,N'-diphenyl-4,4'-diaminodiphenyl and 1,1-bisN,N-di(4-tolyl)amino-phenyl!cyclohexane and hydrazone compounds such as4-diphenyl-aminobenzaldehyde-N,N-diphenylhydrazone. Also used areporphyrin compounds such as copper phthalocyanine.

Although organic electroluminescent elements have high luminescentproperties, they are insufficient in stability during luminescence andin storage stability and have hence not been put to practical use. Asone of the causes of the insufficient stability during luminescence andstorage of the element, the insufficient stability of the chargetransporting material is considered. Since the organic layers of anorganic electroluminescent element are as thin as from 50 to hundreds ofnanometers, an exceedingly high voltage is applied per unit thickness.In addition, heat generation occurs due to luminescence and theapplication of an electric current. The charge transporting material istherefore required to have electrical, thermal, and chemical stability.Furthermore, the charge transporting layer of an element, which layer isgenerally in an amorphous state, undergoes crystallization due toluminescence or long-term storage, whereby luminescence is inhibited orelement breakage is caused. For this reason, the charge transportingmaterial is required to have the property of readily coming into anamorphous or vitreous state and stably retaining this state.

With respect to the compounds proposed for use as a charge transportingmaterial, by which the stability of a luminescent element is affected asdescribed above, the diamine compounds and the porphyrin compounds stillhave the problem that they undergo crystallization to cause elementdeterioration, although these compounds are electrically and thermallystable and some of these attain relatively high luminescent properties.The hydrazone compounds, which have a simple structure, are insufficientin electrical and thermal stability, so that they are not a desirablematerial.

A charge transporting material for use in an organic photoreceptor isrequired not only to enable the photoreceptor to satisfy variousproperty requirements including sensitivity, but also to have chemicalstability so as to withstand light, ozone, and electrical load andfurther have stability or durability so as not to cause a sensitivitydecrease even when the photoreceptor is used repeatedly or over long.

A charge transporting material for use in an organic electroluminescentelement is required not only to enable the element to satisfy variousproperty requirements including luminescent properties, but also havegood film-forming properties so as to impart excellent stability duringluminescence and storage to the organic electroluminescent element andalso have stability so as to withstand heat, oxygen, and electricalload.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel hydrazonecompound useful as a charge transporting material, with which anelectrophotographic photoreceptor having satisfactory photoreceptorproperties and high sensitivity and durability and an organicelectroluminescent element excellent not only in luminescent propertybut in stability during luminescence and storage can be obtained.

Another object of the present invention is to provide anelectrophotographic photoreceptor and an organic electroluminescentelement both of which contain the hydrazone compound.

The present invention provides a hydrazone compound represented by thefollowing formula (I), an electrophotographic photoreceptor which has aphotosensitive layer containing the compound on an electricallyconductive support, and an organic electroluminescent element containingthe compound as a charge transporting material. ##STR2##

In formula (I), Ar₁ represents a substituted or unsubstituted phenylenegroup, a substituted or unsubstituted naphthylene group, a substitutedor unsubstituted biphenylene group, or a substituted or unsubstitutedanthrylene group, Ar₂ represents a substituted or unsubstituted arylgroup, R₁ and R₂ each independently represents a hydrogen atom, ahalogen atom, an unsubstituted alkyl group, or an unsubstituted alkoxygroup, R₃ represents an unsubstituted alkyl group, a substituted orunsubstituted aralkyl group, or a substituted or unsubstituted arylgroup, Z represents an ethylene group or a vinylene group, and n is 0 or1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a single-layer electrophotographicphotoreceptor.

FIG. 2 is a sectional view of a single-layer electrophotographicphotoreceptor containing a charge generation material dispersed therein.

FIG. 3 is a sectional view of an electrophotographic photoreceptorcomprising a charge generation layer and a charge transporting layerformed in this order on an electrically conductive support.

FIG. 4 is a sectional view of an electrophotographic photoreceptorcomprising a charge transporting layer and a charge generation layerformed in this order on an electrically conductive support.

FIG. 5 is a sectional view of an electrophotographic photoreceptorhaving a protective layer.

FIG. 6 is a sectional view of an organic electroluminescent element.

FIG. 7 is an infrared absorption spectrum of Compound No. 2.

FIG. 8 is an infrared absorption spectrum of Compound No. 21.

FIG. 9 is an infrared absorption spectrum of Compound No. 1.

FIG. 10 is an infrared absorption spectrum of Compound No. 22.

DETAILED DESCRIPTION OF THE INVENTION

The hydrazone compound represented by formula (I) will be described inmore detail below.

Ar₁ represents a phenylene group, a naphthylene group, a biphenylenegroup or a anthrylene group, which may have a substituent(s).

Ar₂ represents an aryl group which may have a substituent(s). Examplesof the unsubstituted aryl group include a phenyl group, a naphthylgroup, a biphenyl group, an anthryl group, and a pyrenyl group.

R₁ and R₂ each independently represents a hydrogen atom, a halogen atom,an unsubstituted alkyl group (preferably having 1 to 4 carbon atoms), oran unsubstituted alkoxy group (preferably having 1 to 4 carbon atoms).

R₃ represents an unsubstituted alkyl group (preferably having 1 to 6carbon atoms), an aralkyl group which may have a substituent(s), or anaryl group which may have a substituent(s).

Examples of the substituent with respect to Ar₁, Ar₂ and R₃ describedabove include an alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, a chlorine atom and a bromine atom.

The hydrazone compound represented by formula (I) described above, whichmay be used as a charge transporting material in the present invention,is a novel compound. In general, this compound is synthesized from thecorresponding aldehyde compound and hydrazine compound throughcondensation. For example, the hydrazone compound can be obtained byreacting an aldehyde compound represented by the following formula (II):##STR3## (wherein Ar₁, R₁, R₂, Z, and n have the same meanings as informula (I)) with a hydrazine derivative represented by the followingformula (III): ##STR4## (wherein Ar₂ and R₃ have the same meanings as informula (I)) at a temperature of 10° to 120° C., preferably 25° to 80°C., in an organic solvent inert to the reactants, e.g., toluene,alcohol, acetone, N,N-dimethylformamide, dimethyl sulfoxide,tetrahydrofuran, or dioxane. If desired, use may be made of an acidcatalyst such as p-toluenesulfonic acid, hydrochloric acid, sulfuricacid, or acetic acid or a reaction accelerator such as sodium acetate.

Alternatively, the hydrazone compound may be obtained by reacting analdehyde compound represented by formula (II) described above with ahydrazine derivative represented by the following formula (IV): ##STR5##(wherein Ar₂ has the same meaning as in formula (I)) at a temperature of10° to 120° C., preferably 25 to 80° C., in an organic solvent inert tothe reactants, e.g., toluene, alcohol, acetone, N,N-dimethylformamide,dimethyl sulfoxide, tetrahydrofuran, or dioxane, if desired in thepresence of an acid catalyst such as p-toluenesulfonic acid,hydrochloric acid, sulfuric acid, or acetic acid or a reactionaccelerator such as sodium acetate, to thereby obtain a hydrazonecompound represented by the following formula (V): ##STR6## (whereinAr₁, Ar₂, R₁, R₂, Z, and n have the same meanings as in formula (I)),and then reacting this hydrazone compound with an alkylating,aralkylating, or arylating agent represented by the following formula(VI):

    R.sub.3 X                                                  (VI)

(wherein R₃ has the same meaning as defined above and X represents achlorine atom, a bromine atom, an iodine atom, and a sulfonic acidresidue) at a temperature of 10° to 200° C., preferably 30° to 120° C.,in an organic solvent inert to the reactants, e.g., toluene, xylene,dichlorobenzene, nitrobenzene, N,N-dimethylformamide,N-methylpyrrolidone, alcohol, or dioxane, in the presence of adeacidifying agent such as, e.g., sodium hydroxide, potassium hydroxide,sodium hydrogen carbonate, potassium hydrogen carbonate, sodiumcarbonate, potassium carbonate, triethylamine, or pyridine.

The following are examples of the compound of the present invention,which examples can be used as a charge transporting material. ##STR7##

The electrophotographic photoreceptor of the present invention has aphotosensitive layer containing one or more hydrazone compoundsrepresented by formula (I). The photosensitive layer of theelectrophotographic photoreceptor of the present invention may have anyof various possible constitutions. Photoreceptors having representativephotosensitive-layer constitutions are shown in FIGS. 1 to 5.

The photoreceptor shown in FIG. 1 comprises a conductive support 1 andformed thereon a photosensitive layer 2 comprising the hydrazonecompound, a sensitizing dye, and a binder resin.

The photoreceptor shown in FIG. 2 comprises a conductive support 1 andformed thereon a photosensitive layer 21 comprising acharge-transporting medium 3 comprising the hydrazone compound and abinder resin and a charge generation material 4 dispersed in acharge-transporting medium 3. In this photoreceptor, the chargegeneration material generates charges upon light absorption and thecharges are transported by the charge-transporting medium. It isdesirable that the charge transporting material does not absorb thelight which the charge generation material absorbs to generate charges.The hydrazone compound shows only a little light absorption in part ofthe range of from the ultraviolet region to the low-wavelength visibleregion, and therefore satisfies the condition that its absorptionwavelength region does not overlap with that of a charge generationmaterial.

In the photoreceptors shown in FIGS. 1 and 2, the thickness of thephotosensitive layer is preferably from 10 to 25 μm.

The photoreceptor shown in FIG. 3 comprises a conductive support 1 andformed thereon a photosensitive layer 22 made up of a charge generationlayer 5 consisting mainly of a charge generation material 4 and a chargetransporting layer 3 comprising the hydrazone compound and a binderresin. In this photoreceptor, the light which has passed through thecharge transporting layer 3 reaches the charge generation layer 5, wherethe light is absorbed by the charge generation material 4 to generatecharges. These charges are injected into the charge transporting layer 3and transported.

The photoreceptor shown in FIG. 4 has a photosensitive layer 23 which isthe same as the photosensitive layer of the photoreceptor shown in FIG.3 except that the positions of the charge generation layer 5 and thecharge transporting layer 3 are reversed. The mechanism of chargegeneration and charge transportation in this photoreceptor is the sameas in the above photoreceptor.

The photoreceptor shown in FIG. 5 has a photosensitive layer 24 which isthe same as the photosensitive layer of the photoreceptor shown in FIG.4 except that it further has a protective layer 6 formed on the chargegeneration layer 5 for the purpose of improving mechanical strength.

In the photoreceptors shown in FIGS. 3, 4 and 5, the thickness of thecharge generation layer is preferably 2 μm or less, and the thickness ofthe charge transporting layer is preferably 5 to 25 μm. The thickness ofthe protective layer is preferably 2 μm or less.

The amount of the hydrazone compound in the hydrazonecompound-containing layer is generally from 30 to 70% by weight,preferably from 40 to 60% by weight.

The amount of the sensitizing dye in the photosensitive layer shown inFIG. 1 is generally from 0.1 to 5% by weight. The amount of the chargegeneration material in the photosensitive layer shown in FIG. 2 isgenerally from 1 to 30% by weight. The amount of the charge generationmaterial in the charge generation layers shown in FIGS. 3, 4 and 5 isgenerally from 20 to 90% by weight. The sensitizing dye andelectron-withdrawing compound each can be used generally in an amount of0.1 to 5% by weight.

These photoreceptors according to the present invention may be producedby ordinary methods. For example, the hydrazone compound represented byformula (I) described above is dissolved in an appropriate solvent alongwith a binder resin. If desired, a charge generation material, asensitizing dye, an electron-withdrawing compound, a plasticizer, apigment, and other additives are added to the solution. The coatingfluid thus prepared is applied to a conductive support and dried to forma photosensitive layer having a thickness of several micrometers to tensof micrometers to thereby produce a photoreceptor. A photosensitivelayer having a double-layer structure comprising a charge generationlayer and a charge transporting layer can be produced by applying theabove-described coating fluid on a charge generation layer, or byforming a charge generation layer on a charge transporting layer formedfrom the above-described coating fluid by coating. If desired, anadhesive layer, an interlayer, or a barrier layer may be formed in thephotoreceptors thus produced.

Examples of the charge generation material which can be used in thepresent invention include any conventional charge generation materialsuch as azo compounds, bisazo compounds, trisazo compounds, tetrakisazocompounds, thiapyrylium salts, squarilium salts, azulenium salts,cyanine dyes, perylene compounds, metal-free or metal phthalocyaninecompounds, polynuclear quinone compounds, thioindigo compounds, andquinacridone compounds

Examples of the solvent which can be used for the preparation of thecoating fluid include polar organic solvents such as tetrahydrofuran,1,4-dioxane, methyl ethyl ketone, cyclohexanone, acetonitrile,N,N-dimethylformamide, and ethyl acetate, aromatic organic solvents suchas toluene and xylene, and chlorinated hydrocarbon solvents such asdichloromethane and dichloroethane. Solvents in which the hydrazonecompound and the binder resin are highly soluble are preferred.

Examples of the sensitizing dye include triarylmethane dyes such asMethyl Violet, Brilliant Green, Crystal Violet, and Acid Violet,xanthene dyes such as Rhodamine B, Eosine S, and Rose Bengale, thiazinedyes such as Methylene Blue, pyrylium dyes such as benzopyrylium salts,thiapyrylium dyes, and cyanine dyes.

Examples of the electron-withdrawing compound which forms a chargetransfer complex in cooperation with the hydrazone compound includequinones, e.g., chloranil, 2,3-dichloro-1,4-naphthoquinone,1-nitroanthraquinone, 2-chloroanthraquinone, and phenanthrenequinone,aldehydes, e.g., 4-nitrobenzaldehyde, ketones, e.g.,9-benzoylanthracene, indandione, 3,5-dinitrobenzophenone,2,4,7-trinitrofluorenone, and 2,4,5,7-tetranitrofluorenone, acidanhydrides, e.g., phthalic anhydride and 4-chloronaphthalic anhydride,cyano compounds, e.g.,tetracyanoethylene, terephthalalmalenonitrile, and9-anthrylmethylidenemalenonitrile, and phthalide derivatives, e.g.,3-benzalphthalide and3-(α-cyano-p-nitrobenzal)-4,5,6,7-tetrachlorophthalide.

Examples of the binder resin include various resins compatible with thehydrazone compound, such as homopolymers and copolymers of vinylcompounds, e.g., styrene, vinyl acetate, vinyl chloride, acrylic esters,methacrylic esters, and butadiene, poly(vinyl acetal)s, polycarbonates,polyesters, poly(phenylene oxide)s, polyurethanes, cellulose esters,phenoxy resins, silicon resins, and epoxy resins. The binder resin isused in an amount of usually from 0.4 to 10 times by weight, preferablyfrom 0.5 to 5 times by weight, the amount of the hydrazone compound.

A known plasticizer may be incorporated into the photosensitive layer ofthe present invention for the purpose of improving film-formingproperties, flexibility, and mechanical strength. Examples of theplasticizer include phthalic esters, phosphoric esters, chlorinatedparaffins, methylnaphthalene, epoxy compounds, and chlorinated fattyesters.

The conductive support on which the photosensitive layer is formed maybe a material for use as the support of a known electrophotographicphotoreceptor. Examples of the support include drums or sheets of ametal, e.g., aluminum, stainless steel, or copper; substrates obtainedby laminating or vapor-depositing such a metal; plastic films or drumsand paper sheets or tubes to each of which electrical conductivity hasbeen imparted by coating with a conductive substance, e.g., a metalpowder, carbon black, copper iodide, or a polymeric electrolyte, alongwith an appropriate binder; and plastic films or drums to each of whichelectrical conductivity has been imparted by incorporating such aconductive substance.

According to the present invention, an organic electroluminescentelement is also obtained which contains the hydrazone compoundrepresented by the above-described formula (I) as a hole-transportinglayer.

Organic electroluminescent elements have a two-layer or three-layerstructure sandwiched between a transparent electrode serving as a baseand a counter electrode. The two-layer structure is a combination of ahole-transporting layer and an electron-transporting luminescent layeror a combination of an electron-transporting layer and ahole-transporting luminescent layer. The three-layer structure comprisesa luminescent layer sandwiched between a hole-transporting layer and anelectron-transporting layer.

The layer constitution according to the present invention may be eithera two-layer structure comprising a hole-transporting layer and anelectron-transporting luminescent layer (as a luminescent layer) or athree-layer structure comprising a hole-transporting layer, anelectron-transporting luminescent layer or an hole-transportingluminescent layer (as a luminescent layer), and an electron-transportinglayer. Each layer generally has the thickness of 20 to 300 nm.

The hole-transporting layer is made of the hydrazone compound of formula(I) of the present invention and has a thickness of generally from 20 to300 nm, preferably from 30 to 200 nm.

FIG. 6 shows an organic electroluminescent element having the two-layerstructure.

The organic electroluminescent element shown in FIG. 6 comprises asupport 7 and, formed thereon in this order, a transparent electrode 8,a hole-transporting layer 9, an electron-transporting luminescent layer10, and an electrode 11.

Examples of an electron-transporting luminescent material includechelated oxinoide compounds, e.g., tris(8-quinolinol)aluminum, bis(8-quinolinol)magnesium, and tris(5-chloro-8-quinolinol)gallium,coumarin derivatives, perylene pigments, chelated 2,2'-bipyridinecompounds, and chelate compounds of salicylidene-o-aminophenolderivatives.

Examples of an electron transporting material include2-(4-tert-butylphenyl)-5-(4-biphenylyl )-1,3,5-oxadiazole,2,4,7-trinitro-9-fluorenone,4-butoxycarbonyl-9-dicyanomethylidene-fluorene,3,3'-bis(tert-butyl)-5,5'-dimethyl-4,4'-diphenoquinone,3,5'-bis(tert-butyl)-5,3'-dimethyl-4,4'-diphenoquinone, and3,5-bis(tert-butyl)-3',5'-dimethyl-4,4'-diphenoquinone.

Examples of a hole-transporting luminescent material include4,4'-bis(2,2-diphenylvinyl)biphenyl4-styryl-4',4"-dimethoxytriphenylamine and 4,4'-bis5-(p-dimethylaminophenyl)-1,3,4-oxadiazol-2-yl!biphenyl.

The support of the organic electroluminescent element may be a glass, aplastic, quartz, etc. A metal, e.g., gold, aluminum, indium, silver, ormagnesium, an indium-tin oxide (ITO), tin oxide, zinc oxide, or the likeis deposited as a thin layer on the support by vapor deposition to givea translucent or transparent electrode. A charge transporting layer(i.e., a hole-transporting layer and a electron-transporting layer) anda luminescent layer are formed on the electrode by vapor deposition, andanother electrode is further formed thereon in the same manner as theabove to thereby produce an organic electroluminescent element. Thiselement is caused to luminesce by applying a direct voltage thereto.

The present invention will be explained below in more detail byreference to the following Examples, but the invention should not beconstrued as being limited thereto. Otherwise indicated, all parts andpercentage are by weight.

EXAMPLE 1 Synthesis of Compound No. 2

In 500 parts of tetrahydrofuran were dissolved 29.9 parts of 4-5-(10,11-dihydro-5H-dibenzo b,f!azepinyl)!-benzaldehyde and 24.3 partsof N,N-diphenylhydrazine hydrochloride. This solution was stirred at 50°C. for 2 hours. After completion of the reaction, the reaction mixturewas poured into 2,000 parts of water, and the crystals precipitated weretaken out by filtration. The crystals obtained were washed with ethylalcohol and then dried at reduced pressure. These crystals were purifiedby column chromatography (carrier, silica gel; eluent,toluene/hexane=1/2 by volume) to obtain 27.3 parts (yield, 58.6%) of 4-5-(10,11-dihydro-5H-dibenzo b,f!-azepinyl)!benzaldehydeN,N-diphenylhydrazone. This compound had a melting point of 196.0° to197.0° C. The results of elemental analysis are shown in Table 1 below,together with calculated values for C₃₃ H₂₇ N₃.

                  TABLE 1    ______________________________________               C (%)     H (%)   N (%)    ______________________________________    Calculated value                 85.1        5.8     9.0    Found value  85.3        6.0     9.2    ______________________________________

The infrared absorption spectrum (KBr tablet method) of the compoundobtained is shown in FIG. 7.

EXAMPLE 2 Synthesis of Compound No. 17

In 500 parts of tetrahydrofuran were dissolved 29.7 parts of 4-5-(5H-dibenzo b,f!azepinyl)!benzaldehyde and 13.4 parts ofN,N-methylphenylhydrazine. One part of glacial acetic acid was addedthereto, and this solution was stirred at 50° C. for 3 hours. Aftercompletion of the reaction, the reaction mixture was poured into 2,000parts of water, and the crystals precipitated were taken out byfiltration. The crystals obtained were washed with ethyl alcohol andthen dried at reduced pressure. The crystals dried were recrystallizedfrom ethyl acetate to obtain 28.9 parts (yield, 72.0%) of 4-5-(5H-dibenzo b,f!azepinyl)!benzaldehyde N,N-methylphenylhydrazone. Thiscompound had a melting point of 195.0° to 197.0° C. The results ofelemental analysis are shown in Table 2 below, together with calculatedvalues for C₂₈ H₂₃ N₃.

                  TABLE 2    ______________________________________               C (%)     H (%)   N (%)    ______________________________________    Calculated value                 83.8        5.8     10.5    Found value  83.4        6.1     10.3    ______________________________________

The infrared absorption spectrum (KBr tablet method) of the compoundobtained is shown in FIG. 8.

EXAMPLE 3 Synthesis of Compound No. 1

In 500 parts of tetrahydrofuran were dissolved 21.0 parts of 4-5-(10,11-dihydro-5H-dibenzo b,f!azepinyl)!benzaldehyde and 12.0 parts ofN,N-methylphenylhydrazine. One part of glacial acetic acid was addedthereto, and this solution was stirred at room temperature for 3 hours.After completion of the reaction, the reaction mixture was poured into2,000 parts of water, and the crystals precipitated were taken out byfiltration. The crystals obtained were washed with ethyl alcohol andthen dried at reduced pressure. These crystals were purified by columnchromatography (carrier, silica gel; eluent, toluene/hexane=2/3 byvolume) to obtain 15.8 parts (yield, 55.8%) of 4-5-(10,11-dihydro-5H-dibenzo b,f!-azepinyl)!benzaldehydeN,N-methylphenylhydrazone. This compound had a melting point of 192.0°to 194.0° C. The results of elemental analysis are shown in Table 3below, together with calculated values for C₂₈ H₂₅ N₃.

                  TABLE 3    ______________________________________               C (%)     H (%)   N (%)    ______________________________________    Calculated value                 83.3        6.3     10.4    Found value  83.4        6.4     10.4    ______________________________________

The infrared absorption spectrum (KBr tablet method) of the compoundobtained is shown in FIG. 9.

EXAMPLE 4 Synthesis of Compound No. 18

In 500 parts of tetrahydrofuran were dissolved 23.8 parts of 4-5-(5H-dibenzo b,f!azepinyl)!benzaldehyde and 26.5 parts ofN,N-diphenylhydrazine hydrochloride. This solution was stirred at roomtemperature for 3 hours. After completion of the reaction, the reactionmixture was poured into 2,000 parts of water, and the crystalsprecipitated were taken out by filtration. The crystals obtained werewashed with ethyl alcohol and then dried at reduced pressure. Thecrystals dried were dissolved in 100 parts of ethyl acetate, and thissolution was poured into 1,000 parts of methyl alcohol to recrystallizethe reaction product. Thus, 28.9 parts (yield, 77.9%) of 4-5-(5H-dibenzo b,f!azepinyl)!benzaldehyde N,N-diphenylhydrazone wasobtained. This compound had a melting point of 178.0° to 179.0° C. Theresults of elemental analysis are shown in Table 4 below, together withcalculated values for C₃₃ H₂₅ N₃.

                  TABLE 3    ______________________________________               C (%)     H (%)   N (%)    ______________________________________    Calculated value                 85.5        5.4     9.1    Found value  85.3        5.6     9.0    ______________________________________

The infrared absorption spectrum (KBr tablet method) of the compoundobtained is shown in FIG. 10.

EXAMPLE 5

To 18.5 parts of an 8% THF solution of a polyester resin (Vylon 200,manufactured by Toyobo Co., Ltd., Japan) was added, as a chargegeneration material, 1.5 parts of Chlorodiane Blue (Compound A) havingthe following structure. ##STR8##

This mixture was placed in an agate pot containing agate balls, and thispot was rotated for 1 hour in a planetary grinder (manufactured byFritsch Co.) to disperse the charge generation material. Analuminum-deposited PET film serving as a conductive support was coatedon the aluminum side with the above-obtained dispersion by means of awire-wound bar coater. The coating was dried first at 60° C. andordinary pressure for 2 hours and then at reduced pressure for 2 hoursto form a charge generation layer having a thickness of 0.3 μm.

On the other hand, 1.5 parts of Compound No. 1 as a charge transportingmaterial was added to 18.75 parts of an 8% dichloroethane solution of apolycarbonate resin (Panlite K-1300, manufactured by Teijin ChemicalsLtd., Japan). Ultrasonic wave was applied to this mixture to completelydissolve the hydrazone compound. This solution was applied to the chargegeneration layer with a wire-wound bar coater, and the coating was driedfirst at 60° C. and ordinary pressure for 2 hours and then at reducedpressure for 2 hours to form a charge transporting layer having athickness of about 20 μm. Thus, photoreceptor No. 1 was produced.

The sensitivity of this photoreceptor was measured with an electrostaticcopying paper tester (trade name "EPA-8100," manufactured by KawaguchiDenki Seisakusho K. K., Japan) as follows. First, the photoreceptor wascharged in the dark with -8 kV corona discharge. The resultingphotoreceptor was exposed to white light at 3.0 lx to measure the time(sec) required for the surface potential to decrease to a half of theinitial surface potential value. Thus, the half decay exposure, E_(1/2)(lx.sec), was determined. This photoreceptor had an initial surfacepotential of -1,090 V and an E_(1/2) of 1.7 lx.sec.

EXAMPLES 6 TO 18

Photoreceptor Nos. 2 to 14 were produced in the same manner as inExample 5, except that the charge generation material (Compounds A, B, Cand D) and charge transporting material (hydrazone compound) werechanged as shown in Table 5.

The results of the evaluation of photoreceptor Nos. 2 to 14 are given inTable 6.

                  TABLE 5    ______________________________________                       Charge       Charge             Photo-    Transporting Generation    Example  receptor  Material     Material    No.      No.       Compound No. Compound No.    ______________________________________     6       2          2           A     7       3          5           A     8       4         10           B     9       5         14           B    10       6         16           B    11       7         17           A    12       8         18           A    13       9         21           A    14       10        26           B    15       11        30           B    16       12        32           B    17       13         1           C    18       14         1           D    ______________________________________

                  TABLE 6    ______________________________________    Photo-       Initial Surface    receptor     Potential   E.sub.1/2    No.          (-V)        (1x · sec)    ______________________________________    2            1010        1.9    3            920         2.3    4            874         2.0    5            855         1.8    6            1005        1.8    7            1033        1.7    8            843         1.9    9            998         2.7    10           1220        1.9    11           980         2.1    12           1100        2.0    13           720         1.6    14           984         1.7    ______________________________________     ##STR9##

EXAMPLE 19

To 50 parts of a 3% THF solution of a poly(vinyl butyral) resin (S-LecBX-L, manufactured by Sekisui Chemical Co., Ltd., Japan) was added 1.5parts of α-TiOPc as a charge generation material. This mixture wastreated with an ultrasonic dispersing machine for 45 minutes to obtain adispersion. An aluminum-deposited PET film serving as a conductivesupport was coated on the aluminum side with the above-obtaineddispersion by means of a wire-wound bar coater. The coating was driedfirst at 60° C. and ordinary pressure for 2 hours and then at reducedpressure for 2 hours to form a charge generation layer having athickness of 0.3 μm.

On the other hand, 1.5 parts of Compound No. 1 as a charge transportingmaterial was added to 18.75 parts of an 8% dichloroethane solution of apolycarbonate resin (Panlite K-1300, manufactured by Teijin ChemicalsLtd.). Ultrasonic wave was applied to this mixture to completelydissolve the hydrazone compound.

This solution was applied to the charge generation layer with awire-wound bar coater, and the coating was dried first at 60° C. andordinary pressure for 2 hours and then at reduced pressure for 2 hoursto form a charge transporting layer having a thickness of about 20 μm.Thus, photoreceptor No. 15 was produced.

The sensitivity of this photoreceptor was measured with an electrostaticcopying paper tester (trade name "EPA-8100") as follows. First, thephotoreceptor was charged in the dark with -8 kV corona discharge. Theresulting photoreceptor was exposed to 800-nm monochromatic light at alight quantity of 0.4 μW/cm² to measure the quantity of energy requiredfor the surface potential to decrease to a half of the initial surfacepotential value. Thus, the half decay exposure, E_(1/2) (μJ/cm²), wasdetermined. This photoreceptor had an initial surface potential of-1,085 V and an E_(1/2) of 0.51 μJ/cm².

EXAMPLE 20

Photoreceptor No. 16 was produced in the same manner as in Example 19,except that the following trisazo compound was used as a chargegeneration material in place of α-TiOPc. ##STR10##

The sensitivity of this photoreceptor was measured in the same manner asin Example 19. As a result, this photoreceptor was found to have aninitial surface potential of -1,125 V and an E_(1/2) of 0.48 μJ/cm².

EXAMPLE 21

To 125 parts of an 8% dichloroethane solution of a polycarbonate resin(Panlite K-1300, manufactured by Teijin Chemicals Ltd.) were added 0.1part of the following thiapyrylium salt as a charge generation material##STR11## and 10 parts of Compound No. 18 as a charge transportinglayer. Ultrasonic wave was applied to this mixture to completelydissolve the thiapyrylium salt and the hydrazone compound. Analuminum-deposited PET film serving as a conductive support was coatedon the aluminum side with the above-obtained solution by means of awire-wound bar coater. The coating was dried first at 60° C. andordinary pressure for 2 hours and then at reduced pressure for 2 hoursto form a photosensitive layer having a thickness of 15 μm. Thus,photoreceptor No. 17 was produced.

The sensitivity of this photoreceptor was measured with an electrostaticcopying paper tester (trade name "EPA-8100") as follows. First, thephotoreceptor was charged in the dark with +8 kV corona discharge. Theresulting photoreceptor was exposed to white light at 3.0 lx to measurethe time (sec) required for the surface potential to decrease to a halfof the initial surface potential value. Thus, the half decay exposure,E_(1/2) (lx.sec), was determined. This photoreceptor had an initialsurface potential of +890 V and an E_(1/2) of 2.8 lx.sec.

EXAMPLE 22

An aluminum-deposited PET film was coated on the aluminum side with thecoating fluid of a charge transporting material which fluid had beenused in Example 5, by means of a wire-wound bar coater. The coating wasdried first at 60° C. and ordinary pressure for 2 hours and then atreduced pressure for 2 hours to form a charge transporting layer havinga thickness of 10 μm.

On the other hand, 3.0 parts of the same disazo compound as used inExample 17 was added as a charge generation material to 18.5 parts of an8% THF solution of a polyester resin (Vylon 200, manufactured by ToyoboCo., Ltd.). This mixture was placed in an agate pot containing agateballs, and this pot was rotated for 1 hour in a planetary grinder(manufactured by Fritsch Co.) to disperse the charge generationmaterial. To this dispersion was added 200 parts of THF. The resultingmixture was stirred to give a coating fluid, which was then applied tothe charge transporting layer by spraying. The coating was dried firstat 60° C. and ordinary pressure for 2 hours and then at reduced pressurefor 2 hours to form a charge generation layer having a thickness of 0.5μm. This charge generation layer was further coated by spraying with asolution obtained by dissolving an alcohol-soluble polyamide resin inisopropanol. The coating was dried first at 60° C. and ordinary pressurefor 2 hours and then at reduced pressure for 2 hours to form an overcoatlayer having a thickness of 0.5 μm. Thus, photoreceptor No. 18 wasproduced.

The sensitivity of this photoreceptor was measured in the same manner asin Example 5. As a result, this photoreceptor was found to have aninitial surface potential of 1,030 V and an E_(1/2) of 2.2 lx.sec.

COMPARATIVE EXAMPLE 1

A comparative photoreceptor was produced in the same manner as inExample 5, except that the following hydrazone compound ##STR12## wasused in placed of Compound No. 1 used in Example 5.

The sensitivity of this photoreceptor was measured in the same manner asin Example 5. This photoreceptor had an initial surface potential of-970 V and an E_(1/2) of 4.5 lx.sec. The results show that the hydrazonecompound used, in which the hyrdazine moiety has a closed ring structure(i.e., Ar₂ and R₃ are bonded to each other to form a ring), has a lowdrift mobility and hence brought about the low sensitivity.

EXAMPLE 23

An ITO glass electrode (transparent conductive film of standard type;manufactured by Matsuzaki Shinku K. K., Japan) was set on the substrateholder of a vapor deposition device (Type LC-6F, manufactured by ShinkuKikai Kogyo K. K., Japan), and Compound No. 2 (4-5-(10,11-dihydro-5H-dibenzo b,f!azepinyl)!-benzaldehydeN,N-diphenylhydrazone) was placed on the heating board. The vacuumchamber was evacuated to 1×10⁻⁶ Torr. The heating board was heated andvapor deposition was conducted at a rate of 12 nm/min to form on the ITOglass electrode a 50 nm-thick hole-transporting layer made of CompoundNo. 2. Subsequently, tris(8-quinolinol)aluminum was placed on theheating board, which was then heated to conduct vapor deposition at arate of 20 nm/min to form a 50 nm-thick luminescent layer on thehole-transporting layer. A 150 nm-thick magnesium layer was furtherformed thereon by vapor deposition at a rate of 40 nm/min, giving acounter electrode. Thus, an organic electroluminescent element wasproduced.

A 12-V direct current was applied to the element, with the ITO electrodeas the positive electrode and the magnesium electrode as the negativeelectrode. As a result, the element emitted a bright green luminescence.The luminance of this light was measured with a luminance meter (TypeLS-110, manufactured by Minolta Camera Co., Ltd., Japan), and was foundto be 1,600 cd/m². A continuous illumination test was further performedat a luminance of 500 cd/m². As a result, the luminance half-life periodof this element was 200 hours.

EXAMPLE 24

An organic electroluminescent element was produced in the same manner asin Example 23, except that Compound No. 17 (4- 5-(5H-dibenzob,f!azepinyl)!benzaldehyde N,N-methylphenylhydrazone) was used in placeof Compound No. 2. A 13-V direct current was applied to this element. Asa result, the element emitted a bright green luminescence at a luminanceof 1,400 cd/m². A continuous illumination test was further performed ata luminance of 500 cd/m². As a result, the luminance half-life period ofthis element was 220 hours.

The novel hydrazone compound of the present invention has excellenthole-transporting ability and can be widely utilized as ahole-transporting material. The electrophotographic photoreceptor of thepresent invention having a photosensitive layer containing the hydrazonecompound on a conductive support shows excellent photoreceptorproperties and can be advantageously utilized widely as anelectrophotographic photoreceptor. Furthermore, the organicelectroluminescent element of the present invention produced using thehydrazone compound as a hole-transporting material, which compound formsa thermally stable satisfactory thin film, shows excellent luminescentproperties and can be advantageously utilized widely as a displayelement.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. An electrophotographic photoreceptor having aphotosensitive layer on an electrically conductive support, saidphotosensitive layer containing a hydrazone compound represented byformula (I): ##STR13## wherein Ar₁ represents a substituted orunsubstituted phenylene group, a substituted or unsubstitutednaphthylene group, a substituted or unsubstituted biphenylene group, ora substituted or unsubstituted anthrylene group, Ar₂ represents asubstituted or unsubstituted aryl group, R₁ and R₂ each independentlyrepresents a hydrogen atom, a halogen atom, an unsubstituted alkylgroup, or an unsubstituted alkoxy group, R₃ represents an unsubstitutedalkyl group, a substituted or unsubstituted aralkyl group, or asubstituted or unsubstituted aryl group, Z represents an ethylene groupor a vinylene group, and n is 0 or
 1. 2. The electrophotographicphotoreceptor of claim 1, said photosensitive layer further comprising abinder resin.
 3. The electrophotographic photoreceptor of claim 2,wherein the amount of the binder resin is 0.4 to 10 times by weight theamount of the hydrazone compound.